The invention relates to a device suitable for manufacturing an optical registration carrier, such as a master plate, which device comprises a support for said optical registration carrier, at least a first and a second light source, wherein the wavelengths of the light from said first and said second light source are different from each other, as well as an objective disposed between said light sources and said support, which is movable with respect to said light sources.
The term master plate is understood to mean a plate which can be used for making a mould that is used for manufacturing CD""s, DVD""s and the like by means of an injection moulding process. It is also possible, however, to use the master plate itself as a mould. The term optical registration carrier as used in the present patent application refers to a master plate as well as to a CD or DVD or the like, unless indicated otherwise.
In a device referred to in the introduction, which is known per se, a light source having a relatively small wavelength is used for writing the optical registration carrier to be manufactured. Said light source will hereinafter be called the writing light source. Another light source having a greater wavelength is used for focussing the writing light source. This light source will hereinafter be called the focussing light source.
The advantage of this arrangement is that it makes it possible to select the optimum wavelength of the light source for the required writing or focussing function. In addition, when writing on an optical registration carrier including a photosensitive lacquer it is possible to select a wavelength for the focussing light source to which said photosensitive lacquer is insensitive.
The two light sources direct their beams at the optical registration carrier to be worked via the same objective, to which end the focal points of the two light sources need to coincide. During focussing, the objective is moved with respect to the light sources and with respect to the support of the optical registration carrier until the focussing light source is accurately focussed on the optical registration carrier. Since the two light sources have different wavelengths, also the focal distances of the objective are different for these different wavelengths. When the objective is moved with respect to the focussing light source, also its position with respect to the writing light source changes. The consequence of this is that when the differences between the wavelengths of the light sources are relatively large, the writing light source cannot be kept focussed when the objective is being moved for focussing the focussing light source.
The object of the invention is to provide a device wherein light sources having different wavelengths can be focussed simultaneously in a simple manner.
This objective is accomplished with the device according to the invention in that a correction lens is disposed between the first light source and the objective, which correction lens can be moved jointly with the objective, wherein the focal points of the two light sources will at least substantially coincide with various movements of the objective and the correction lens with respect to the light source.
By means of the correction lens the light beam from the first light source is caused to converge or diverge relative to the light beam from the second light source in such a manner that the two light beams are focussed at the same point after exiting the objective. By moving the objective jointly with the correction lens, the focal points of the two light sources will coincide in every position of the objective with respect to the light source.
Preferably the two light sources are lasers, with the first light source being a focussing laser and the second light source being a writing laser. The wavelength of the focussing laser is preferably greater than that of the writing laser. The first light source must converge between the correction lens and the objective thereby.